I hope People Services and Human Resources people across government are beginning to recognise the potential of the service for reaching professional people as potential hires and to connect past employees back to organisations through alumni networks (you never know when you might be able to lure them back).
While on the topic, it is also worthwhile for agencies to keep an eye on services like Glassdoor, which allows employees to anonymously rate their organisations (yes there are agencies reviewed in the site) and is also growing as a recruitment tool.
Twitter is also becoming a tool for highlighting positions to potential staff (used by the Australian Department of Human Services in a coordinated way for graduates, and by other agencies on an ad hoc basis) and several agencies have used Facebook for advertising (such as ASIO) and managing graduate groups (such as the Department of Finance and Deregulation and the Australian Department of Human Services).
Blogs are also being used (such as by the Department of Health and Ageing).
In fact, if your organisation is not using social media to attract staff, perhaps you're being outcompeted for skills by those organisations who do.
If your recruitment team still isn't sold on the value of Web 2.0 and social media as a useful recruitment and retention tool for organisations, point them in the direction of Michael Specht's 52 ideas for Social Media for HR professionals.
This ideas sheet identifies a range of techniques available to "support key HR and Recruitment processes. Including the use of Twitter, blogs for employees, wikis to create organisational polices and social bookmarking to identify talent pools.".